FERTILIZING THE IRISH POTATO CROP
By BAYARD F. FLOYD and R. W. RUPRECHT
Florida is peculiar in that it grows a wide variety of crops,
and in that each of these is grown largely around certain centers
where they form the chief cash crops for those communities.
The conditions governing the locations are, character of soil and
subsoil, presence of flowing artesian water, freedom from cold,
and others.
The Irish or white potato is grown largely in the Hastings
section, which includes adjoining parts of St. Johns and Putnam
Counties. The acreage in this section varies from year to year.
In 1918 the total potato area in the state was about 35,000 acres,
of which approximately 13,000 acres were included in the Hast-
ings district. Other important potato centers are near Kissim-
mee, Moore Haven, Miami and Plant City. Small plantings are
made thruout the state.
Outside the section bordering Lake Okeechobee, the potatoes
are planted largely upon sandy loam soil of the type known
locally as flatwoods soil. In the Hastings district the soil is
underlain at an average depth of one to three feet by a rather
heavy sandy clay subsoil.
This subsoil affords a particular advantage in that it allows
a cheap form of sub-irrigation. At times, when the crops are in
need of moisture, the water from artesian wells is run onto the
land. In most of the district these wells are easily obtainable at
a depth of 200 feet or more. The water spreads from the ditches,
covering the top of the subsoil from whence it rises by capillary
attraction to the loamy soils above.
The sandy loam soils in the Hastings section and other sec-
tions are lacking in humus and particularly in the elements of
fertility, ammonia, phosphoric acid and potash. The following
is an analysis of a sample collected in part of the experimental
field receiving no fertilizer. The sample was collected in a low
area and is probably more fertile than the higher soils.
Ammonia ..-......-...................-........ .107 percent
Phosphoric acid ............-------............ .027 percent
Potash .............................-........-- .048 percent

(Note:-The experiments herein reported were planned and conducted
by B. F. Floyd until May 1, 1920, when R. W. Ruprecht took charge.)

Florida Agricultural Experiment Station

For the successful growing of potatoes on a commercial
scale, long practice has proven it necessary to' increase the
amounts of these plant food elements in the soil by the application
of commercial fertilizers. While this is a well established fact,
there is much difference of opinion and a lack of exact informa-
tion concerning what sources of these elements to use in making
up the fertilizers, what formulas to use, and what elements to
apply for the most profitable crop production.
Before the World War sources of potash fertilizers were
plentiful and cheap, and they were used more or less liberally.
But after the beginning of the war, when they became scarce and
expensive, there was much questioning of the profitableness of
their use. Many growers and farmers omitted them entirely
from their fertilizers; others used them sparingly; and no one
used them liberally.
During the first year of the scarcity there was much specu-
lation concerning the effects of the omission or reduction of pot-
ash in the fertilizers. At the end of the year when no detri-
mental effects were seen, many were of the opinion that it was
present in the soil in sufficient quantities for good crop produc-
tion and doubted the profitableness of using potash in their
fertilizers. Later, however, differences in yield and carrying
qualities of the crops caused some to question this conclusion.
Logically, the farmers and fruit growers of Florida looked
to their agricultural experiment station for answers to the many
questions concerning this situation. Unfortunately it had not
been possible to carry out experiments to obtain this infor-
mation.
In the fall of 1917, thru the efforts of the late J. A.
Stevens of DeLand, a cooperative arrangement was perfected
between F. M. Leonard & Co. of Boston, Mass., and the Florida
Agricultural Experiment Station to carry out some fertilizer
experiments with Irish potatoes on the plantation of the former
at Hastings, Florida, to obtain information that would answer
some of these questions.
Two experiments were outlined in the spring of 1918. The
purpose of one was to study the results to be obtained from the
use of raw Florida phosphate and of acid phosphate as sources
of phosphoric acid in fertilizers for Irish potatoes, as compared
with those obtained where no phosphate was used. The purpose
of the otherwas to study the results to be obtained from the use
of fertilizers containing various percentages of potash in com-

Bulletin 158, Fertilizing the Irish Potato Crop

prison with those obtained where no potash was used. Both
experiments were to be carried out on virgin land that had never
received any fertilizer.

CONDITIONS COMMON TO THE TWO EXPERIMENTS
The experiments were carried out on the Leonard plantation
at Hastings, Florida, on a 10-acre tract, forming part of a 60-
acre field, all of which was planted in potatoes. Figure 2 shows
the arrangement of the plots. At the beginning of the experi-
ment in the spring of 1918, the land was virgin and newly cleared,
never having received any fertilizer. The soil was a sandy loam
underlain at a depth of from one to three feet by a sandy clay.
The lay of the land was practically level. There were, how-
ever, sufficient variations to cause some scattering low spots in
the field where the plants were sufficiently injured during heavy
rains to reduce the yield. This injury, however, was kept at a
minimum by the digging of shallow ditches to drain these areas
when necessary.
The potatoes were planted in east and west rows or mounds
on the beds. There were ten rows on each bed during the sea-
son of 1918, and nine during 1919. The number of rows to each
bed was reduced in 1919 in order to make higher mounds.
This was made necessary on account of heavy rains at the
beginning of the season.
The beds were separated by shallow ditches that connected
on the west end of the field with an irrigation ditch and at the
east end of the field with a drainage ditch.

Florida Agricultural Experiment Station

An artesian well was located on the west side of the field
and provided irrigation water when necessary.
Spaulding Rose No. 4 potatoes obtained from Maine were
used for planting. The following table shows the time of fer-
tilizing, planting and harvesting during the respective seasons:

The labor of caring for the experimental field formed part
of the regular routine of the Leonard plantation. Therefore, the
land was prepared and the crop planted, cultivated and sprayed
in exactly the same manner as the other fields on the planta-
tion.
The plants were sprayed at regular intervals with bordeaux
mixture to prevent blight. The spraying proved particularly
helpful during 1919 when both early blight and late blight of
potatoes was very prevalent in nearby unsprayed fields.
WEATHER CONDITIONS
Weather conditions varied greatly in 1918, 1919 and 1920.
There was a drought during the early half of 1918, making it
necessary to irrigate the fields; while in March, April and May
there were heavy rains that flooded the fields, doing some dam-
age. In 1919 the conditions were somewhat the reverse. There
was plenty of moisture in the soil early in the season, but
drought conditions prevailed during the latter part of the year.
In 1920 about one week after the potatoes were planted, a
heavy three-day rain flooded the fields, making replanting neces-
sary. As it was thought the heavy rains probably washed out
most of the soluble ammonia, all the plots were top dressed on
March 19, 1920, with nitrate of soda at the rate of 180 pounds
to the acre. The weather during the harvesting season was very
wet and digging was delayed several weeks.

SBulletin 158, Fertilizing the Irish Potato Crop 7

HARVESTING AND GRADING
The potatoes were dug with a digging machine, gathered by
hand, placed in crates, and taken to the packing shed where they
were graded by machine. Four different grades were made. On
the basis of weight, the different grades averaged as follows:
No. 1, 6 potatoes to the pound; No. 2, 11 to the pound; No. 3, 19
to the pound, and No. 4, 35 to the pound.
TABLE 2.-ANALYSIS OF FERTILIZER USED ON PLOTS CONTAINING NO
PHOSPHORIC ACID

FERTILIZERS USED
The constitution of the mixed fertilizers used in this ex-
periment is shown in tables 2 and 3. The fertilizers were mixed
by machinery at the factory and applied by hand in the field. A
sand filler was used in mixing them so that equivalent weight
would carry the same amounts of a particular plant food. The
different mixtures were used at the rate of. 1,700 pounds an acre
during 1918, and 1,530 pounds during 1919 and 1920.
The raw phosphates, soft phosphates and finely ground
pebble phosphate, were applied in amounts carrying total phos-
phoric acid equivalent to three times the available phosphoric
acid in the mixtures where acid phosphate was the source of
phosphoric acid. On this basis the soft phosphate was used at
the rate of 1,570 pounds an acre, and the pebble phosphate at
the rate of 1,275 pounds an acre.

MANNER OF APPLYING FERTILIZER
Table 1 shows the time of application of the fertilizer used
in the two experiments. In 1918 the raw phosphates were mixed
with the soil in the rows or mounds. At the end of the season
the mounds over the whole field were leveled. In 1919 and 1920
the raw phosphates were broadcasted before the land was broken
in preparation for the crop.
The mixed fertilizers were applied by hand and mixed with
soil in the row.
PLOTS
The experimental field consisted of 10 beds extending en-
tirely across the field from east to west. Approximately one
acre was included in each bed. During 1918 only the first seven
beds on the south were included in the experiment.
In 1919 the three beds on the north side, adjoining the seven
beds used in the experiments in 1918, were plotted and added to
the experiments. Since the sequence of the fertilizer treatment
of these three beds were different from the remainder of the field,
the results obtained on them will be discussed separately under
the heading "Extension of Experiments."
Ten one-tenth acre plots were measured off on each bed. By
this division there were 70 one-tenth acre plots in the experiment
field in 1918 and 100 in 1919 and 1920.
A north and south line was established dividing the field
into halves. This line was coincident with the line between the
fifth and sixth plots on each bed. That part of the field west of

Bulletin 158, Fertilizing the Irish Potato Crop

this line was included in the phosphate experiment, that part
east in the potash experiment.
In 1919 and 1920, excepting the plots in the extension ex-
periments, the fertilizer treatment given each plot in the two
experiments was exactly the same as in 1918. The plan of the
experiments contemplates this repetition for a period of at least
five years. This bulletin is, therefore, only a progress report of
the two experiments.

THE PHOSPHATE EXPERIMENT
The purpose of this experiment, as stated, was to study the
results to be obtained from the use of raw Florida phosphates
and of acid phosphate as sources of phosphoric acid in fertilizers
for Irish potatoes planted on virgin land never before receiving
any fertilizer, as compared with those where practically no phos-
phate at all was included in the fertilizer used.
In that part of the field included in this experiment and be-
ginning on the south, all of the plots on the odd beds received a
fertilizer containing about 5 percent ammonia and 21/2 percent
potash, but practically no phosphoric acid. Owing to the fact
that the tankage and the cottonseed meal contained some phos-
phoric acid, the mixture was not entirely free from phosphoric
acid but carried between one-half and one percent of this element.
(See table 2.)
The plots on the even beds received mixtures containing 5
percent ammonia, 21/2 percent potash and 8 percent available
phosphoric acid where acid phosphate was used as the source
of phosphoric acid; or 24 percent total phosphoric acid where
either of the raw phosphates were used. The plots on the even
beds were so arranged that each particular mixture was used
five times at regular intervals in the field. Thus each plot,
receiving a fertilizer mixture containing phosphoric acid, was
flanked on either side by plots receiving mixtures without phos-
phoric acid. Tables 2 and 3 show the analyses of the fertilizer
mixtures used.
RESULTS IN 1918, 1919, 1920
Tables 4, 5 and 6 show the yields in pounds and by grades
for tenth-acre plots, and the treatment of the different plots.
Tables 7, 8 and 9 show the average yield calculated to barrels an
acre using 165 pounds as equivalent to one barrel.

Florida Agricultural Experiment Station

TABLE 4.-YIELDS IN POUNDS AND BY GRADES OF THE PHOSPHATE
AND NO PHOSPHATE TENTH-ACRE PLOTS, 1918

It will be noted that the yields in 1918 were very low on all
of the plots. This was probably due to the newness of the land.
In 1919 and 1920 the yields of all of the plots were much better
and those from the acid phosphate plots approached the average
yield of the fields not included in the experiment. Both pebble
phosphate and soft phosphate have shown striking increases in
yield as compared to those obtained where no phosphate was
used. In 1920 the total yield where pebble phosphate was used
was nearly equal to that of the acid phosphate plots; but the
amount of No. 1 grade potatoes was slightly less where the for-
mer was used.
While the initial cost of the pebble phosphate was about the
same as the acid phosphate the total cost was somewhat greater
for the pebble phosphate because it was applied separately from
the rest of the fertilizer.
GROWTH OF THE PLANTS
The growth from the tubers in 1918 on the plots receiving
fertilizer mixtures without phosphate and in those receiving

Bulletin 158, Fertilizing the Irish Potato Crop

mixtures with the raw phosphates, was somewhat irregular, giv-
ing a poor stand of plants. Late in the season plants here and
there were just breaking thru the.soil. It was also noticed
that after the plants in these plots became independent of the
tubers, growth was checked. After a period of several weeks,
the plants in the raw phosphate plots increased rapidly in size,
but by the end of the season had not become quite as large as
those in the acid phosphate plots.
In the plots which received no phosphate the plants made
slow growth thru the entire season. At the end of the growing
season they averaged fully 50 percent smaller in size than those
in the acid phosphate plots. The character of growth was also
different. The leaves were somewhat undersized, and the inter-
nodes of the stems were longer. The plants had a rather stiff,
upright appearance. Early in the season their color was slightly
yellowish; later it became a deep green. The plants were slow
in maturing. At the end of the season the majority of plants were
still alive and making some growth, while the tops in the other
plots were all dead.
This condition of slow growth is apparently coupled with a
lack of available phosphoric acid and indicates the need of this
material in the vegetative growth of the plants, particularly in
the early stages.
In 1919 the differences in growth of the plants in the plots
receiving acid phosphate and those receiving the raw phosphates
and no phosphoric acid, were practically the same as in 1918. The
same slowness of growth in the plants receiving the raw phos-
phates and no phosphoric acid was noted, but this was not at all
so pronounced in the former as in 1918.
The sprouting of the tubers was not as slow this year as
in 1918. There was practically a perfect stand of plants. The
plants receiving acid phosphate were large, bushy, stocky and of
a normal green color. Many showed strong branches from the
lower nodes that formed strong stalks with well formed leaves
and leaf stalks. Those receiving raw phosphates were practically
of the same type but were not as large. There were fewer plants
that showed branching. The plants on the plots receiving no
phosphate were undersized, slender, spiky and of an abnormal
green color. The leaves were undersized, curled and upright,
giving a mouse-eared appearance. It is assumed that this type of
growth is indicative or characteristic of phosphoric acid hunger.
Also a slowness of maturity in the plants receiving no phosphate

Florida Agricultural Experiment Station

was again observed. The plants in these plots were still alive
and growing when all the plants in the other plots were prac-
tically dead.
In 1920 the plants receiving acid phosphate made a bushy
growth that was normal in all respects. The plants receiving
pebble phosphate were not quite so good, while those receiving
soft phosphate were distinctly less bushy and somewhat slender
in growth. The plants receiving no phosphoric acid were much
undersized but did not show the slender, spiky growth as in 1919.
It is assumed that the more favorable soil moisture condition,
prevalent during 1920, allowed enough phosphate in the soil to
become available to avoid the starvation phenomena as shown in
1919.
On May 25, 1920, the plants in the acid phosphate plots
were all dead. While those in the no phosphate plots were still
alive and growing. The plants in the plots receiving the raw
phosphates were somewhat intermediate. Groups of plants here
and there on these plots, particularly the pebble phosphate plots,
were dead. This indicates that soluble phosphoric acid is con-
ducive to early plant maturity.
INFLUENCE OF FERTILIZERS ON SUCCEEDING CROPS
After the potatoes were harvested in 1918 the mounds were
leveled and the beds planted to cowpeas by broadcasting. No
fertilizer was applied as it was assumed that there was a suf-
ficient amount left in the soil from that used on the potatoes to
make this crop.
The vines made a luxuriant growth on all the plots that had
received phosphate, regardless of the source. Those on the plots
that had received no phosphate grew very much as the potatoes
did on these plots. When the vines became independent of the
seed, the growth became slow and continued so thruout the
season. At the end of the season the vines were only from 50 to
60 percent as high as those on the phosphate plots.
Figure 1 shows the dividing line between two plots. The
one in the foreground was given no phosphate, whereas the one
in the background received acid phosphate. The difference in
height is indicated by the distance between the man's hands.
The same differences in color and maturity that were noticed
in the potatoes were also present in the cowpeas. The vines
were slightly yellow early in the season, but from normal to deep
green later. When the vines were all dead on the phosphate plots,
many were still alive and growing on the plots that had received
no phosphate.

Bulletin 158, Fertilizing the Irish Potato Crop 15

Unfortunately, it was not possible to obtain a record of the
yield of seed on the different plots. After the crop had matured
the vines were plowed under to improve the soil.
After the potatoes were harvested in 1919 the land was
planted to corn. Owing to excessive rains the crop was
a failure. A crop of grass and weeds developed on the land.
This was plowed under to add humus. In 1920 the land was al-
lowed to grow up to weeds and grass, following the harvesting of
the potatoes.
THE POTASH EXPERIMENT
The purpose of this experiment was to study the results to
be obtained from the application of fertilizers containing various
percentages of potash for Irish potatoes planted on virgin land,
in comparison with those obtained where no potash fertilizers
were used. The experiment was carried out on virgin land that
had never received any fertilizer.
This experiment occupied the east half of the field mentioned.
Seven beds were included in the experiment. Beginning on
the south, all the plots on the odd beds were given a fertilizer
mixture containing about 5 percent of ammonia, 8 percent of
available phosphoric acid and no potash. The plots on the even
beds were given fertilizer mixtures containing the same amounts
of ammonia and phosphoric acid and 1 percent, 3 percent, and 5
percent respectively of potash. The plots were so arranged that
each particular mixture was used at regular intervals in the field
five times (see Fig. 2). Thus each plot receiving a fertilizer
mixture containing potash was flanked on either side by plots re-
ceiving mixtures with no potash.
TABLE 10.-ANALYSIS OF FERTILIZER ON 1 PERCENT POTASH PLOT

In 1918 the yield of the whole field was low, probably because
the land was new. The yields have been increasing yearly as the
land has been improved by the addition of humus and probably
by the accumulation of fertilizer residues. The differences be-
tween the application of various, amounts of potash have been
very uniform. The largest increase each year was with the 1
percent potash, while the 5 percent has given an increase over
the 3 percent which only a little more than covered the cost of
the additional 2 percent. The increase in yield in every case was
largely of first grade potatoes which makes the value of the in-
crease greater.
INFLUENCE UPON GROWTH OF TOPS
In 1918 the plants receiving no potash produced practically
as good top growth as those receiving potash. The character of
the growth was bushy, with well developed foliage of good
color.

Florida Agricultural Experiment Station

SYMPTOMS OF POTASH STARVATION
In the season of 1919 an entirely different situation occurred.
The plants receiving no potash fertilizer made a very poor
growth and developed certain appearances evidently character-
istic of potash starvation in plants.
During the first half of the season the plants in the no
potash plots made a normal growth and apparently were just
as vigorous and thrifty as those receiving potash. Early in
April, 1919, it was noticed that the plants on the beds where no
potash was applied were beginning to show a deeper green color
than those on the other beds, and that they were not growing
quite as fast. As the season progressed this appearance be-
came more intensified until the beds without potash showed as
dark green bands across the field. The plants became stunted
and were lacking in business. At the end of the season they
averaged fully 25 percent smaller in size than those receiving
potash.
After the crop was 40 days old plants here and there
began to develop an inward curling of the margins of the leaves
with more or less crinkling of the tissue between the larger
veins. The surfaces of the leaves showed a waxy sheen as if they
had been polished with parafin. In later stages of growth there
was a bronzing of the surfaces of the leaves and a dying of the
tissue in spots along the margins and toward the tips. As the
season progressed, the condition became more widespread until
it was general on all the beds without potash. It was noticed,
however, that in spots here and there the trouble was not so
pronounced, or it was entirely absent. This was probably due
to variations in the soil and to the fact that these areas contained
sufficient potash to supply the needs for the top growth.
The fact that the crop in 1918 made a good top growth but
failed to make a good crop of tubers, and that the symptoms of
potash hunger did not develop in 1919 until the plants had almost
attained full size and had begun to set tubers, indicates that the
virgin land contained enough potash for the top growth in 1918.
It also indicates that the plants draw most heavily upon the
supply of potash in the soil during their late growth when the
tubers are being made, and that only small amounts of potash
are needed during the early growth of the crop.
In 1920 the plants in the plots receiving no potash were
somewhat undersized and showed a distinctly darker green color
than did those receiving potash. Thus the field had the same

Bulletin 158, Fertilizing the Irish Potato Crop

banded appearance that it did in 1919. But the plants showed
none of the acute symptoms of potash hunger as they did in
1919. It is assumed that either the better soil moisture condi-
tion in 1920 made some of the residual potash available for the
plants; or that the soda from the top dressing of nitrate of soda
acted to some extent as a substitute for the potash.
Very little difference in growth could be seen in the plants
receiving various amounts of potash. The chief difference
seemed to be in the tuber production.
On May 25 the plants in the no potash plots were all dead,
while those on the plots receiving potash were just beginning to
die. Apparently the lack of balance with potash allowed the
phosphoric acid effect to predominate, so that the plants in these
plots reached an earlier maturity.
SUCCEEDING CROP
After the crop was harvested in 1918 the mounds were
leveled and the field planted to cowpeas. The vines made as good
growth where no potash was applied as where applied. It was
not possible to get a record of the yield. After the plants died
they were plowed under to improve the soil. In 1919 corn was
planted but it was a failure because of excessive rains. No suc-
ceeding crop was planted in 1920. The field was allowed to grow
a volunteer crop of grass and weeds.
GREENHOUSE EXPERIMENTS
Early in the season of 1919 experiments were begun in the
greenhouse at the Experiment Station, Gainesville. Fertilizers
from the lot used at Hastings were used here. (See tables 10,
11, 12 and 13.) The soil used was a sandy loam from a field that
had been cropped repeatedly with velvet beans and other crops,
but it had never been given any fertilizer. In these experiments
the potato plants in every plot where potash was not applied,
developed the same symptoms as did those in the field at Hast-
ings during that year. The symptoms appeared at about the
same stage of growth but were not pronounced. Every plant
showed evidence of potash hunger.
These experiments confirm the results obtained in the field
in 1919. It is probable that the stronger development of the
symptoms was caused by the soil used. Since it had been re-
peatedly cropped without the addition of fertilizer, there was not
sufficient available potash for a normal development of the
plants.

Florida Agricultural Experiment Station

EXTENSION OF EXPERIMENTS
Ten beds of approximately one acre each were included in.
the potato experimental field in 1919 and 1920. (See page 5.)
During 1918 only the first seven beds on the south were used
(Fig. 2). The remaining three beds formed a part of an adjacent
field planted to potatoes and were given the same amount and
about the same kind of fertilizer mixture, containing acid phos-
phate, as was used in the phosphate experiment. It analyzed
5 percent ammonia, 8 percent available phosphoric acid, and 21/2
percent potash.
In 1919 the three beds were plotted and given the same
fertilizer treatment as the plots in the phosphate and the potash
experiments. The arrangement and treatment of the plots is
shown in figure 1. From the arrangement of these it is seen
that there is only one bed, where no phosphate and no potash
was used in 1919, that is exactly comparable with the plots re-
ceiving potash or phosphate during that year.

EXTENSION OF PHOSPHATE EXPERIMENT
In 1918 all plots on the three beds in the experiment received
the fertilizer mixture containing acid phosphate. In 1919 all
plots on the middle one of the three beds received the mixture
containing no phosphate (Fig. 2). Thus the sequence of treat-
ment for these plots are acid phosphate in 1918 and no phosphate
in 1919 and 1920. By comparing the yields from these plots with
those in the phosphate experiment proper that received no phos-
phate in 1918 and in 1919, an indication can be obtained of the
influence of the residual phosphoric acid in the soil from the
preceding season upon the succeeding crop.
The plots on the remaining two beds were given fertilizer
mixtures containing acid phosphate, pebble phosphate and soft
phosphate respectively. The treatments were so alternated that
each of the mixtures were used on three or four different plots on
the beds (Fig. 2). Thus there is the following different sequences
of treatment on the three beds in the experiment:
Acid Phosphate, 1918.........--.......Acid Phosphate, 1919 and 1920;
Acid Phosphate, 1918................Pebble Phosphate, 1919 and 1920;
Acid Phosphate, 1918..........--....--Soft Phosphate, 1919 and 1920;
Acid Phosphate, 1918......................No Phosphate, 1919 and 1920.

RESULTS
Tables 20 and 21 show the yields in pounds and by grades of
the phosphate and adjacent no phosphate tenth-acre plots on the
three beds. Table 22 shows the average yields in barrels an acre
of the three beds in 1918; those of the different phosphate plots
in 1919 and 1920; and the 1920 yield of the plots in phosphate
experiment proper which had received no phosphate at any time.
Comparing the 1920 yield of first grade potatoes obtained
where acid phosphate was used in 1918 and no phosphate in 1919
and 1920 with that where no phosphate was used at all, a dif-
ference of eight barrels is seen. This increase is apparently due
to the residual phosphoric acid from the 1918 application. Where
acid phosphate was used during all three years the increase
amounts to nearly 13 barrels.
Soft phosphate substituted for acid phosphate during the
second and third years of the experiment failed to keep up the
yield of the first grade potatoes. The yield obtained here was
little better than that where no phosphate was applied during
the second and third years. This is probably due to the lack of
soluble phosphoric acid in this material. Pebble phosphate gave
-somewhat better results.
The growth of the plants during 1919 and 1920 on the plots
given raw phosphates during the second and third years was not
as good as that where acid phosphate was used both years, but it
was much better than that on the plots receiving no phosphate

Bulletin 158, Fertilizing the Irish Potato Crop

in 1919 and 1920. The growth on the plots receiving acid phos-
phate in 1918 and no phosphate in 1919 and 1920, was markedly
better than that on the plots that received no phosphate during
the'three years, and was more comparable with that on the plots
receiving the raw phosphates in 1919 and 1920. While there was
a reduction in growth in the plants on the plots receiving acid
phosphate in 1918 but no phosphates in 1919 and 1920, practi-
cally none of the starvation phenomena seen in the plants that re-
ceived no phosphate during the three years were observed here.
EXTENSION OF POTASH EXPERIMENT
The three beds adjacent to the potash experiment on the
north were included in the extension of potash experiment in
1919 (Fig. 2). In 1918 these plots received a fertilizer analyzing
about 5 percent ammonia, 8 percent available phosphoric acid
and 21/2 percent potash, which was the same as that given the
acid phosphate plots in the phosphate experiment. (Table
3, page 7.) While this fertilizer contained the same amount of
ammonia that was contained in the fertilizers applied to the
potash experiment, it was derived from more sources. Also the
percentage of potash in it was different from that in any formula
used in the potash experiment, but was nearest the 3 percent
potash formula. (Table 9.)
In 1919 the beds were plotted and all the plots on the middle
bed were given the no potash fertilizer mixture. The plots on
the other beds received fertilizers containing 1 percent, 3 percent
and 5 percent respectively of potash (Fig. 1).
TABLE 23.-YIELD IN POUNDS AND BY GRADES OF POTASH AND
ADJACENT No POTASH TENTH-ACRE PLOTS, 1919
(21% Potash 1918) (2z% Potash 1918)
S 1% Potash 1919 No Potash 1919
Grades .............. I 1 2 3 4 1 | 2 3 4
157 80 47 81 289 133 44 20
Pounds -............ 318 138 39 21 292 162 48 24
408 180 39 32 316 189 62 33
Total ..-....... 883 398 125 134 897 484 154 77
Average ............ 294 133 42 45 299 161 51 26

Table 23 and 24 show the 1919 and 1920 yields in pounds on
tenth-acre plots; and by grades of the plots that received 21/2
percent potash in 1918, and 1 percent, 3 percent and 5 percent re-
spectively in 1919 and 1920. Table 25 shows (1) the average
yields of the three beds in 1918; (2) the average yields of the
plots in the extension experiment as shown in tables 23 and 24;
(3) the average yields of the plots in the potash experiment that
received no potash; all calculated to barrels an acre.
INFLUENCE OF RESIDUAL POTASH ON 1919 AND 1920 CROPS
The results of this experiment show the influence of residual
potash from the 1918 application upon the crop of the succeeding
years, 1919 and 1920. The fertilizer applied in 1918 contained 21/2
percent of potash. The application was uniform over all the
beds.
In 1920 those plots, receiving 21/2 percent potash in 1918
and no potash in 1919 and 1920, gave a yield of first grade po-
tatoes which was 2.3 barrels an acre greater than the plots in the
adjacent potash experiment that received no potash during the
three years. The plots receiving 1 percent potash in 1919 and
1920 gave an increase of 11.7 barrels, while those receiving 3
percent and 5 percent potash gave increases of 18.4 and 24.3
barrels respectively.
The plants in this- experiment made practically a uniform
growth. None of the symptoms of potash hunger seen in the
potash experiment were noticed on the plots that received no
potash in 1919.

RESUME
From the results obtained thus far in these experiments a
fertilizer analyzing four to five percent ammonia, eight percent
available phosphoric acid and three to five percent potash would
be a balanced and economical fertilizer.
The experiments do not give any conclusion concerning the
best amount of fertilizer to be used on an acre, nor what sources
or combination of sources of ammonia and potash is best. While
the sources of ammonia used give good results, it is possible that
other sources added to the combination might give better results.
For example, no source of immediately available ammonia was
used in the experiments. A better growth and yield as a whole
might have been obtained by using nitrate of soda as one of the
sources of ammonia.

Florida Agricultural Experiment Station

The yield of potatoes in the experiment as a whole has been
low. This is only partly explained by the newness of the land.
While this is true, the variations in the yields caused by the dif-
ferent fertilizer treatments have been pronounced, so that the
factor of low yield probably has not been an interference.
The experiments prove that both phosphoric acid and potash
are limiting factors for growth and crop production in this
region, and must be supplied in the form of fertilizers in order
to produce the most profitable crop.
CONCLUSIONS
The results show further that:
1. Soluble phosphoric acid was necessary in the early
stages of growth to produce vigorous plants.
2. Raw rock phosphates failed to produce maximum top
growth.
3. Pebble phosphates in 1920 gave a yield that was nearly
as great as from acid phosphate.
4. Soft phosphate has not proven as good as the pebble
phosphate.
5. In absence of sufficient potash tubers did not reach full
size, and in extreme scarcity the normal growth of the tops was
also interfered with and certain appearances characteristic of
potash starvation developed.